Circuit board integrated atomic magnetometer and gyroscope

ABSTRACT

Magnetometers, atomic sensors and related systems, methods and devices are disclosed.

This applications claims priority to and the benefit of U.S. provisionalapplication Ser. No. 62/006,535, filed 2 Jun. 2014, which is herebyincorporated herein by reference in its entirety.

BACKGROUND

The performance of high-sensitivity magnetometers, whether vector orscalar field sensors, and related atomic sensors, is improved when thesensors are isolated from magnetic noise, i.e., magnetic fields that arenot intended to be part of the measurement. Such stray magnetic fieldscan originate from the electronics controlling or related to the deviceitself, including circuit boards and heating elements. We disclosesystems, devices and methods that, among other benefits, reduce theincidence of stray magnetic fields in high-sensitivity magnetometers andatomic sensors.

SUMMARY

A device can be used as a vector atomic magnetic field sensor orgyroscope, in the manner described by U.S. Pat. No. 7,038,450, and/or aBell-Bloom scalar magnetic field sensor as described by U.S. Pat. No.3,495,161, both of which are hereby incorporated herein by reference intheir entireties. Devices disclosed herein include physicalimplementations of a specific system which may be operated in any suchmode, as well as a method of operation.

In some embodiments, such devices can include a sensor assembly having abaseplate upon which all other components are supported, stackedsupports, an alkali metal vapor cell, heater, temperature sensor andinsulation, illumination sources which may act to pump the alkali metalvapor, to probe the alkali metal vapor, to heat the alkali metal vaporcell, or some combination of these three, optical elements includingcollimation lenses, polarization modulators, polarizers, waveplates,and/or mirrors, and a detector for the probe illumination. Such devicescan also include interconnections between the sensor unit and acomputerized control system, the control system itself, and a powersource or interface thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-D schematically shows perspective (FIG. 1A), top (FIG. 1B),side (FIG. 1C), and end (FIG. 1D) views of a magnetometer.

FIGS. 2A-D schematically shows perspective (FIG. 2A), top (FIG. 2B),side (FIG. 2C), and bottom (FIG. 2D) views of a second magnetometer.

FIG. 3 schematically shows a circuit board assembly.

FIG. 4 schematically shows another aspect of a circuit board assembly.

FIGS. 5A-D schematically shows perspective (FIG. 5A), top (FIG. 5B),side (FIG. 5C), and end (FIG. 5D) views of a third magnetometer.

FIGS. 6A-C show three particular embodiments of an optical heater.

FIG. 7 shows schematically the relationship between a control system anda sensor assembly.

FIG. 8 illustrates a feature of a method of data sampling.

FIGS. 9-16 schematically show assemblies configured by bending aflexible substrate.

DETAILED DESCRIPTION OF THE DRAWINGS

The figures and description herein include a number of differentembodiments, the features and properties of any of which can beinterchanged and combined as would be appreciated by one of skill in theart.

FIG. 1 schematically shows perspective, top, side, and end views of aparticular embodiment of a magnetometer. A baseplate underlies the restof the system. The baseplate can be a printed circuit board, which cancarry control electronics, or, in some embodiments, heating elements. Asshown, the baseplate carries two illumination sources and a detector.The illumination sources and detector can be mounted directly on thebaseplate or on structures mounted on the baseplate. If the baseplate isa circuit board, the illumination sources and detector may be directlyoperably connected to a control system through mounting on the circuitboard. As is typical, the circuit board can include a stack ofconductive tracks, pads and vias etched from thin sheets of copper whichare laminated onto a non-conductive substrate, such as fiberglass,polyimide, ceramic, or low-dielectric plastic. A stacked structure ofnon-conductive, non-magnetic material such as glass, fused silica,crystalline material, fiberglass, polyimide, or plastic is mounted onand affixed to the baseplate with an adhesive such as cyanoacrylate,epoxy resin with hardener, cured silicone rubber, or other product. Allcomponents are supported upon this structure, ultimately upon, but notnecessarily directly contacting, the baseplate.

As shown in FIG. 1, light from both illumination sources is directedinto the vapor cell by way of various optical elements. A wide varietyof arrangements of optical elements is possible, as will be appreciatedby one of skill in the art. In the embodiment of FIG. 1, eachillumination source directs light through a collimating lens. In someembodiments, such as the embodiment of FIG. 1, one of the illuminationsources, the pump illumination source, sits directly beneath the vaporcell and illuminates the cell from below. The other illumination source,the probe illumination source, is below and to the side of the vaporcell. The beam from the probe illumination source is reflectedhorizontally into the vapor cell, and then reflected again afteremerging from the vapor cell, down onto a detector, which sits eitherdirectly or indirectly on the baseplate.

The illumination sources can be, for example, lamps, LED's or lasers,including diode lasers, vertical cavity surface emitting lasers(VCSELs), grating stabilized diode lasers, or tapered amplifier lasers,or any other appropriate source of light. The pump and probeillumination sources must emit light having a wavelength near the atomictransition of interest in the alkali element chosen for the vapor cell,for example, the rubidium D1 line at 794.8 nm, or the cesium D1 line at894 nm. In some embodiments, the illumination sources may include amechanism for varying the wavelength, such as a grating, a heatingelement, or a variation in current.

As shown in FIG. 1, the vapor cell is supported on stacked supports,separating the vapor cell physically, vertically, from the baseplate.The vapor cell is generally surrounded by an insulating volume and issupported in thermal contact with a heater. The insulation serves tothermally isolate the vapor cell from its surroundings, except on theside adjacent to the heater, which serves to maintain the vapor cell ata desired temperature. The stacked supports serve to physically separatethe vapor cell from the baseplate and any electronics, to help isolatethe vapor cell both thermally, and electromagnetically. The baseplate,illumination sources, and detector may contain current carrying elementsall of which necessarily create at least some non-zero magnetic field,and at least some heat. Separating the vapor cell from current carryingelements reduces external magnetic noise in the neighborhood of thevapor cell and allows for better thermal control. To achieve thesebenefits, the supports should be non-magnetic and/or thermallyinsulating. The supports may contain air trapped in voids for thermalinsulation, and can be constructed of electrically insulating material.

The vapor cell itself may be fabricated from glass and/or otherinsulating or semiconductor material. Such vapor cells can beconstructed by glassblowing, glass fusing, anodic bonding, glass fritbonding, or other fabrication techniques. The active medium in the cellmay be any isotope of lithium, sodium, potassium, rubidium, cesium,francium, or mercury or any combination of these. The cell may contain abuffer gas in addition to the alkali metal, and this gas may include adiatomic gas such as nitrogen, and any of the noble gases includinghelium, neon, argon, krypton, and xenon. These elements may exist in thecell in any combination. The gas pressure in the cell may be nearatmospheric pressure, or it may be near vacuum pressure, or may be manytimes atmospheric pressure.

The heater is adjacent to and in relatively close thermal contact withthe vapor cell. All components of the heater should be able to withstandtemperatures up to 200° C. Several different heaters are described inmore detail below.

FIG. 2 schematically shows perspective, top, side, and bottom views of asecond magnetometer. Although the arrangement is different from themagnetometer of FIG. 1, many of the elements are the same. Like themagnetometer of FIG. 1, in the magnetometer of FIG. 2 light is emittedvertically from the probe illumination source, is reflected horizontallythrough the vapor cell, and then is reflected down onto an upward facingdetector. The pump illumination source, in this case, emitshorizontally, parallel to the plane of the baseplate. Various opticalelements can be used to optimize the light paths. The vapor cell and itsheater are suspended over an opening through the circuit board. In thisway, the vapor cell is relatively physically isolated from the circuitboard. The suspension is typically made of a thermally insulating,non-magnetic material, e.g., glass, silicone, fiberglass, polyimide,Teflon, or ceramic. Again, the heater will be described in more detailbelow. The magnetometer of FIG. 2 is laid out in a more generally planararrangement, but has many of the same attributes and achieves similarbenefits as the magnetometer of FIG. 1.

The device of FIG. 2 also includes a temperature sensor adjacent to thevapor cell. A temperature sensor may be used to determine the actualtemperature of the alkali metal vapor cell, and this information may beused in a feedback loop to inform the temperature control mechanism inorder to achieve a constant temperature in the cell. Some embodimentsmay not utilize a dedicated temperature sensor, and instead use opticalabsorption of illumination to gauge the cell temperature. If used, thetemperature sensor should be in close thermal contact with the cell, andwithin the insulating envelope. The temperature sensor may include aresistive element which exhibits a change of resistance withtemperature, and electrical connections through which the resistance maybe measured. The temperature sensor may include a thick film printedsubstrate of ceramic or other material such as fiberglass, quartz,macor, alumina, aluminum nitride, boron nitride, polyimide, with filmsof high-resistance paste such as platinum or graphite which may bescreen printed, sprayed, painted or otherwise applied. The design may besuch to cancel externally generated field by printing multiple layersalternating between conductor and dielectric (insulating) layers, asexplained further below.

Alternatively, the temperature sensor may consist of a set of thincopper traces encapsulated in layers of printed circuit board. This mayinclude flexible printed circuit board, consisting of etched coppertraces on a substrate of non-conducting material which may befiberglass, polyimide, ceramic or low-dielectric plastic, with aprotective layer of acrylic, epoxy or teflon-based adhesive. The coppertraces may be laid out in an even number of layers whereupon themajority of the trace in each layer is paired with an identical trace ina very close layer to minimize the externally generated magnetic fieldwhen the same current runs through both traces. The thickness and depthof the traces may be approximately equal, and the linear extent of eachtrace kept to a low value, for example less than 50 times thethickness/depth, in order to minimize the size of thermal eddy currents,as illustrated in FIGS. 3 and 4, which also illustrate the design of anoption for the circuit board baseplate and heaters and are explainedfurther below. If a resistive device, the temperature sensor may share acircuit board with other traces, including the heaters, and a singletrace may be used for both heating and temperature sensing.

In another embodiment, traces can be filamentized, as in a Litz wire forexample, with many narrow, separately electrically insulated filamentsmaking up a single trace. Without wishing to be bound by any particulartheory, it is thought that filamentizing the traces can help to minimizethermal eddy currents. By filamentizing the traces, the possible thermalpaths available to current carriers in the traces are elongated, makingeddy currents less prominent. In other words, the more one dimensionalthe individual insulated conductors, the less volume there is forcurrent carriers to move randomly in loops that create magnetic fields.

Alternatively, the temperature sensing element may consist of anentirely optical device, for example a fiber optic sensor based on theband-gap variation of the absorption spectrum of a semiconductor such asgallium arsenide with temperature. Or the temperature sensing elementmay consist of a thermocouple type sensor, in which a pair of wires ofdissimilar materials, such as the well-known combinations of nickel andchromium (Type K), copper and constantan (Type T), or tungsten andrhenium (Type C), in which a voltage is induced at the junctiondepending on the temperature.

Both the devices of FIGS. 1 and 2 are shown as magnetometers, but one ofskill in the art will recognize that each could easily be altered tofunction as a variety of other atomic sensors such as e.g., gyroscopes.

FIG. 3 schematically shows a circuit board assembly arranged to minimizemagnetic fields. As explained above, in a sensor like those shown inFIGS. 1 and 2, a circuit board may serve multiple purposes: it may be astructural component on which the various other components are mounted,it can of course carry circuitry for operating the system, and in someembodiments it can function as a heater. Even in a highly conductivetrace, electric currents will necessarily create some heat, and ifheating is desired, current could be directed to less conductive, moreresistive materials. Currents naturally produce magnetic fields as well.The strength of the magnetic field can be reduced or minimized bycreating currents whose magnetic fields cancel, for example by arrangingfor anti-parallel currents to be a close together as possible. Thecurrents may be configured to create any desired configuration ofmagnetic field in the location of the sensing volume. For example,currents may be configured in a loop or in multiple parallel loops(similar to Helmholtz coils) and adjusted to produce a magnetic fielddesigned to cancel the earth's magnetic field in the vicinity of thesensor. Alternatively, currents can be configured to produce calibrationfields or any other predetermined field strength or geometry.

FIG. 3 shows a circuit board that is arranged so that the currents willcreate substantially mutually cancelling magnetic fields. A trace iscreated on one side of the circuit board, and a congruent trace iscreated on the opposite side of the circuit board. A via is createdthrough the board at one end of the two traces. Conductive material isdeposited in the via to connect the two traces. The result is a singletrace that will naturally direct current along a particular path on oneside of the circuit board, and in the opposite direction along acongruent path on the opposite side of the circuit board. Theanti-parallel current elements here will result in substantiallycancelling magnetic fields, thus minimizing interference with nearbymagnetic field measurements. This arrangement can be used regardless ofthe function of the current, whether it is for controlling circuitry, orheating, or any other purpose.

FIG. 4 schematically shows another aspect of a circuit board assembly.Two congruent traces are shown, as they would be deployed on oppositesides of the electrically insulating substrate of a circuit board. Thecircuit board has been omitted for clarity. The particular shape of thetraces shown have been optimized in several different ways to minimizethe spontaneous creation of transient magnetic fields. Without wishingto be bound by any theory, it is thought that the particular shapes ofthe traces shown have several properties that tend to reduce theprominence of thermal eddy currents that generate transient magneticfields. The traces shown in FIG. 4 have been designed so as to (1)include a relatively tortuous path from one end to the other, (2) have aheight that is comparable to the width of the trace, for example a ratioof height to width of 0.1 to 10, 0.5 to 2, 0.9 to 1.1, or about 1, and(3) include no straight sections longer than a predetermined length. Themaximum length of a straight section of the trace can be, for example,100, 50, 25, 10 or 5 times the width or height of trace.

Although only two traces are shown in each of FIGS. 4 and 5, multiplepairs of traces can be simultaneously employed in a single system,either adjacent to one another, or in layered or stacked arrangements.

FIG. 5 schematically shows perspective, top, side, and end views of athird magnetometer. The various elements of the magnetometer will nowgenerally be familiar, including a baseplate, illumination sources, avapor cell, a detector, optical elements and a heater, although thelayout of the particular magnetometer shown in FIG. 5 is different thanthose of FIGS. 1 and 2 in that the light from the probe illuminationsource passes through the vapor cell twice, in opposite directions,having been reflected from a mirror behind the vapor cell back toward adetector that is adjacent to the probe illumination source. Thismagnetometer also includes an optical modulator in the optical path ofthe pump beam. The optical modulator will have the capability to varythe polarization state of the pump beam illumination in time via aremote signal. It may consist of an electro-optically active materialand an electrical signal to control it. The optical modulator mayconsist of a material with optical properties that can be controlled bythe application of illumination, such as a polymer film or liquidcrystal doped with a dye such as azobenzene, or a biologically derivedprotein such as bacteriorhodopsin, and an illumination source to effectthe control. Alternatively, the optical modulation may be effected byvariation of an applied magnetic field in the volume of the alkali cell.The magnetometer shown includes a baseplate of solid non-conducting,non-magnetic material such as glass, fused silica, crystalline material,fiberglass, polyimide, or plastic. A stacked structure ofnon-conductive, non-magnetic material such as glass, fused silica,crystalline material, fiberglass, polyimide, or plastic is mounted onand affixed to the baseplate.

The particular embodiment shown in FIG. 5 has been implemented with aminimum of conductive material. Some or all inputs to and/or outputsfrom the sensor can be carried by illumination signals on fiber optics.A distant electronic control system may thus be used to operate thesensor without bringing any currents into the immediate neighborhood ofthe sensor. Or a local set of electronics with a low magnetic signaturemay be used to control the device. Illumination signals may includeillumination for the purpose of pumping the atomic vapor, probing theatomic vapor, heating the atomic vapor cell, and/or effecting modulationof optical properties of other illumination sources. In such a device,optical fibers transmit illumination signals from the sensor unit to thedistant electronics/control unit. In any embodiment of ahigh-sensitivity magnetometer or other atomic sensor, it may bebeneficial to address the system entirely by way of optics.

As explained above, one way of introducing heat into the system is byelectrical resistive heating. A different method involves shining lightonto an absorbent material, which then conducts the resulting heat tothe vapor cell. Some examples of such optical heaters are shownschematically in FIGS. 6A-C. A system that includes an optical heaterwill typically include a dedicated heat illumination source.

An optical heater for the cell may be entirely optical system with noelectric currents, or partially optical. Systems with optical heaterscan include an illumination source, such as a semiconductor laser, anLED, or a fiber optic carrying illumination from a distant source. Insuch embodiments, the illumination source may be directed into a cavityor onto a surface consisting of a material which strongly absorbs theillumination, or of a material which transmits the illumination, coatedwith a thin coating of a material which absorbs the illumination, or, inthe case of a closed cavity, of a material which initially reflects theillumination. In this case, the illumination is blocked from exiting thecavity and the cavity heats up like a blackbody. The material of whichthe heater unit is made will have low electrical conductivity and benon-magnetic, but have a moderate to high thermal conductivity (greaterthan 0.1 W/m-K), and could be a polymer material such as polyimide, athermally conductive ceramic such as aluminum nitride or boron nitride,a semiconductor material such as silicon, or a crystalline material suchas diamond or sapphire. Shown in FIGS. 6A-C are examples of blocks ofmaterial which may be used to trap illumination and effect heating of analkali cell. Illumination is to be directed into the cavity from anillumination source either directly or via an optical fiber or otheroptical elements. As shown in FIG. 6A, the cavity in the optical heaterunit may be of a cylindrical shape such as is made by a drilled holeforming a blind bore. FIG. 6B shows an alternative in which a firstblind bore is drilled and then capped, and a second perpendicular blindbore drilled to connect with the first. FIG. 6C shows a box shape madeby an enclosure of flat-sided plates, the interior of which may be atriangular prism as shown, or another three dimensional shape.

If the heater is not optical, it may be an electrical resistive heater,including a resistive element through which current flows and generatesexcess heat. This may include flexible printed circuit board, consistingof etched copper traces on a substrate of non-conducting material whichmay be fiberglass, polyimide, ceramic or low-dielectric plastic with aprotective layer of acrylic or teflon-based adhesive. All components ofthe heater should be able to withstand temperatures up to 200° C. Thecopper traces may be laid out in an even number of layers whereupon themajority of the trace in each layer is paired with an identical trace ina very close layer to minimize the externally generated magnetic fieldwhen the same current runs through both traces. The thickness and depthof the traces may be approximately equal, and the linear extent of eachtrace kept to a low value, for example less than 50 times thethickness/depth, in order to minimize the size of thermal eddy currents.These concepts regarding the circuit board design for the heaters areillustrated in FIGS. 3 and 4, both of which also apply to the designapproach for some options for the baseplate circuit board and someoptions for the temperature sensor.

Alternatively, the heaters may consist of a substrate of a solidelectrically insulating material such as ceramic or fiberglass, quartz,macor, alumina, aluminum nitride, boron nitride, polyimide, with a filmor films of high-resistance paste such as platinum or graphite which maybe screen printed, sprayed, painted or otherwise applied. The design ofthe film layout shall be to cancel externally generated field byprinting multiple layers alternating between conductor and dielectric(insulating) layers of thin paste upon the thick substrate, and routingcurrents in opposing pairs on adjacent layers.

Regardless of type, the heater will typically be located in suchproximity and thermal connection to the vapor cell (or other element tobe heated) as to efficiently transmit heat to it. The cell and heatermust be configured in such a way as to allow illumination to passthrough at least one side of cell. Possibilities include a heater whichobscures only some of the sides of the cell, or a heater that has a holein the center to pass illumination, or a heater which itself transmitsillumination.

All the various embodiments shown here include passive optical elementsincluding but not limited to lenses, mirrors, diffraction gratings,waveplates, beamsplitters, optical filters, and polarizers. These may beused to set the characteristics of the illumination beams with regard totheir spatial extent, spatial distribution, polarizationcharacteristics, or wavelength. For example, a plano-convex lens may beused to collimate illumination emerging from an illumination source,then a linear polarizer may be used to select a single linearpolarization state of that illumination, and a quarter wave plate may beused to convert the linearly polarized illumination to circularlypolarized illumination which may be used to pump the alkali vapor.

All the various embodiments shown here include a detector in the opticalpath of a probe beam in the sensor. The detector may be located locallyon the sensor or remotely wherein illumination may be coupled to thedetector via an optical fiber. A detector may consist of a photodiodewhich converts the incident illumination to an electrical signalproportional to the amplitude of the incident illumination. The detectormay further consist of a set of components which together form apolarimeter, separately detecting illumination of different polarizationstates. This may be achieved using a segmented photodiode in conjunctionwith either a pair of polarizers set at 90 degrees with respect to oneanother, or a mechanism to separate the polarization states of theillumination and cause them to illuminate different sections of thepolarimeter or different optical fibers. This mechanism could be acrystal beam displacer made of a birefringent material such as YVO4(Yttrium Ortho Vanadate).

The sensors described herein will typically be operably connected to acontrol system. One possible relationship between the control system andthe sensor assembly is illustrated in FIG. 7. The control system islargely physically separate from the sensor assembly, though somecomponents described as parts of the control system may be located onthe sensor assembly and vice versa. The control system can include asource of power, for example, an electrical outlet or a battery. Thecontrol system may employ a field-programmable gate array (FPGA) and/ora microprocessor. The control system may be capable of storing,retrieving and implementing a set of instructions which activate thesensor, and will collect and interpret data which may be used todetermine the magnetic field in the region of the sensor, and/or theorientation of the sensor. Its components include control for the powerof all illumination sources, and may include fine control of thewavelength of some of the illumination sources. The illumination sourcesmay be able to operate in a continuous manner or may be caused to pulseon and off. The on and off pulsing may be synchronized to the Larmorprecession of the alkali metal vapor atoms in the magnetic field whichthey experience. The control system can also include such components asare needed to interpret the illumination signal from the detector. Thesemay include an amplifier, and an analog-to-digital converter. Thecontrol system can include a means for activating the heaters in thesensor, and can include a feedback system which locks the temperature ofthe cell, or an illumination source, based on a measurement of thetemperature of the indicated component made using a temperature sensor.The control system may be capable of operating the sensor in the mannerof a SERF vector magnetic field sensor, a Bell-Bloom scalar magneticfield sensor, or a gyroscope.

The modes of operation may be consistent with the SERF vector magneticfield sensor described in U.S. Pat. No. 7,038,450, or a Bell-Bloomscalar magnetic field sensor as described in U.S. Pat. No. 3,495,161, ora gyroscope. Analog-to-digital converters (ADC's) may be used to samplethe various parameters measurable from the sensor, such as the signallevel of the illumination detector. The ADC's sampling the signal fromthe illumination detector may optionally be configured to sampleasynchronously in a manner that is optimized for determining thedifference between the precession frequency and the pumping frequency-asignal that may be used to control the pumping and determine themagnetic field. The sampling may be done on FPGA-controlled clock whichis phase and frequency locked to the atomic spins. The ADC may beoperated to sample at different points in a given Larmor period andthose different points give different information optimized to minimizeinterference from other sources of drift. The illumination source may bemodulated at the Larmor frequency-when modulated on to the resonance,the absorption is higher, so measured transmission is lower. Whensampling off the resonance, the spin orientation is evaluated, as shownin FIG. 8.

The magnetometer of FIG. 1 illustrates a concept beneficial forconstruction of such a device. One beneficial way of assembling microparts like those in the sensors described above is by robotic vacuumgrip. Such vacuum grip robotics are inefficient at flipping the partsaround a horizontal axis. The magnetometer of FIG. 1 avoids thepossibility of any such flipping by arranging all parts so that theyhave a flat, vacuum addressable surface facing upward, and arranging theparts so that their orientation in the sensor is the same as theorientation in which they typically emerge from fabrication. (As shown,the optical elements on either side of the vapor cell, actually presenta sloped upward face, but could be designed with a horizontal upwardface for this type of assembly.)

In another beneficial mode of construction, the various micro parts of amagnetometer or atomic sensor can be affixed to a flexible substrate 901as shown in FIGS. 9-14. The parts can be, for example, a light source902, a heater 903, and a vapor cell 904, stacked in the appropriateorder by folding the substrate as shown in FIGS. 10 and 12. In order toachieve aligned stacking, the parts can either be spaced apart evenly onthe substrate 901 as shown in FIG. 9, or spaced apart unevenly as shownin FIG. 11. Depending on the properties of the flexible substrate 901 itcould be advantageous to have a heater 903 in direct contact with avapor cell 904 with no intervening substrate. Alternatively, thepositions of the micro parts could be rearranged so that different partsare in direct contact with one another. As shown in FIGS. 13 and 14, anarbitrary number of micro parts 902-906 could be attached to such aflexible substrate 901 and stacked in this way, given appropriatespacing of the parts along the substrate. Although an odd number ofmicro parts is shown in the figures, even numbers, indeed any number, ofmicro parts is equally achievable. Once the flexible substrate is foldedso that the micro parts are appropriately stacked and secured, theflexible substrate could be left in place, or it could be trimmed away.The flexible substrate may be left in place if, for example, it includetraces or other useful or necessary electronic components forcontrolling or otherwise interacting with any of the micro parts.

A flexible substrate could also be configured to carry micro parts insuch a way that, when the flexible substrate is appropriately folded,the parts are not merely stacked, but achieve a more generaladvantageous arrangement of parts. FIG. 15 shows one such arrangement inwhich, when appropriately folded, light sources 1501, 1502, a vapor celland heater, 1503, 1504, and detectors 1505, 1506 are arrangedadvantageously on a flexible substrate 1507 so that both vapor cell andheater are properly illuminated. The flexible substrate need not beconfigured to be folded all in a single plane, as shown in FIGS. 9-15.The substrate can be formed with various tabs and flaps, some of whichare configured to be folded in one place while others are to be foldedin another, possibly perpendicular, plane.

FIG. 16 shows how a flexible substrate 1601 in particular can be used toform a configuration of traces that create a predetermined magneticfield at a desired location. In this case, traces 1602, 1603 areconfigured roughly as Helmholtz coils to create a substantially uniformmagnetic field over a central volume. This would be an advantageousarrangement for cancelling a predetermined background magnetic field,such as the earth's magnetic field.

Summary of Certain Embodiments

An assembly for use in a high-sensitivity atomic sensor can include analkali vapor cell, at least one illumination source configured to emitlight when activated, the emitted light having a first predeterminedrange of wavelengths, a light collector capable of collecting light inthe first predetermined range of wavelengths, and a plurality of opticalelements arranged such that (a) light emitted from the at least oneillumination source is directed to the alkali vapor cell, and (b) lightemerging from the alkali vapor cell is directed to the light collector.

Such an assembly can also include a generally planar electricalinsulator having a top and a bottom, the top and the bottom beingopposed to one another, a top trace on the top of the insulator, abottom trace on the bottom of the insulator, and a through trace, theinsulator defining a via from the top to the bottom, the through tracecontacting both the top trace and the bottom trace and passing throughthe via so that the top trace, bottom trace and through trace form asingle electrically conductive element, wherein the top trace and thebottom trace are congruent so that a current along the singleelectrically conductive element tends to create a self-cancellingmagnetic field.

Such an assembly can also include a generally planar electricalinsulator having a top and a bottom, the top and the bottom beingopposed to one another, a top trace on the top of the insulator, the toptrace having a top trace height and a top trace width, and a bottomtrace on the bottom of the insulator, the bottom trace having a bottomtrace height and a bottom trace width, wherein the ratio of the toptrace height to the top trace width and the ratio of the bottom traceheight to the bottom trace width both being in the range of 0.5 to 2,and the top trace and the bottom trace are congruent so that when equaland oppositely directed currents exist simultaneously in the top traceand the bottom trace, the equal and oppositely directed currents tend tocreate cancelling magnetic fields.

In some such assemblies, the electrically conductive element is inthermal contact with the alkali vapor cell such that when current ispassed through the electrically conductive element, thereby producingheat, the heat is transferred to the alkali vapor cell.

In some such assemblies, the electrically conductive element is in notsubstantially in thermal contact with the alkali vapor cell.

Such an assembly can include an optical heating element and a heatillumination source configured to emit light having a secondpredetermined range of wavelengths when activated, wherein the opticalheating element is in thermal contact with the alkali vapor cell, theoptical heating element includes a light-absorbing material that absorbslight in at least a portion of the second predetermined range ofwavelengths, and the plurality of optical elements are arranged suchthat at least some light emitted from the heat illumination source isdirected to the optical heating element.

In some such assemblies, the optical heating element defines an internalcavity, and substantially all of the at least some light emitted fromthe heat illumination source is directed to internal cavity.

In some such assemblies, the internal cavity is defined at least in partby an internal surface, the internal surface including at least aportion of the light-absorbing material.

In some such assemblies, substantially all surfaces defining theinternal cavity are covered in the light-absorbing material such thatsubstantially all of the light emitted from the heat illumination sourceand directed to the internal cavity is absorbed by the optical heatingelement.

In some such assemblies, light-absorbing material is disposed on asurface of the optical heating element that does not define any portionof the internal cavity.

In some such assemblies, the internal cavity is a blind bore.

In some such assemblies, the internal cavity is a polygonal prism.

In some such assemblies, the optical heating element includes on atleast a portion of the interior surface a material that reflects lightin at least a portion of the predetermined range of wavelengths.

In some such assemblies, a portion of the internal cavity is defined bya material that is (a) substantially transparent to light in at least aportion of the predetermined range of wavelengths and (b) substantiallyabsorbent to light in a different wavelength range.

Such an assembly can include a temperature sensor configured to sensethe temperature at a predetermined location on the assembly, and acontroller that is, configured to receive from the temperature sensorsignals indicative of the temperature at the predetermined location onthe assembly, operably connected to the at least one heat illuminationsource, and configured to activate the at least one illumination sourceso as to illuminate the heating element. In some such assemblies, thetemperature sensor includes substantially no electrical currents.

In some such assemblies, the first predetermined range of wavelengthsand the second predetermined range of wavelengths are identical.

In some such assemblies, the first predetermined range of wavelengthsand the second predetermined range of wavelengths have some wavelengthin common but are not identical.

In some such assemblies, the first predetermined range of wavelengthsand the second predetermined range of wavelengths have no wavelength incommon.

Such assemblies can include an electrical insulator having a surface,and a trace disposed on the surface of the insulator, wherein the traceis configured so that, when a predetermined current is passed throughthe trace, a magnetic field having a desired predetermined geometry andmagnitude is created.

In some such assemblies, the desired predetermined geometry andmagnitude substantially cancels a background magnetic field in apredetermined volume that includes at least a portion of the assembly.The background magnetic field can be manmade, or can be, for example,the earth's magnetic field.

Such assemblies can include an electrical insulator having a surface,and a trace on the surface of the insulator, wherein the trace has afilamentary structure comprising a plurality of electrically insulatedsub-traces. In some such assemblies, the filamentary structure isconfigured to minimize magnetic field fluctuation in a predeterminedvolume that includes at least a portion of the assembly.

A method of assembling a high-sensitivity atomic sensor can includeproviding a substantially planar horizontal substrate, verticallydepositing above the provided substrate the at least one illuminationsource, vertically depositing above the provided substrate the lightcollector, vertically depositing above the provided substrate the alkalivapor cell, and vertically depositing above the provided substrate theplurality of optical elements, wherein after being vertically depositedabove the provided substrate, none of the at least one illuminationsource, the light collector, the alkali vapor cell, and the plurality ofoptical elements is (a) reshaped, or (b) rotated about a horizontalaxis.

A method of assembling a high-sensitivity atomic sensor can includeproviding a flexible, substantially planar substrate, affixing to thesubstrate an alkali vapor cell and at least one other component of theatomic sensor, and bending the flexible substrate so that the alkalivapor cell and the at least one other component of the atomic sensor aresubstantially mutually disposed in a predetermined relative position.

1. (canceled)
 2. An assembly for use in a high-sensitivity atomicsensor, the assembly comprising: an alkali vapor cell; at least oneillumination source configured to emit light when activated, the emittedlight having a first predetermined range of wavelengths; a lightcollector capable of collecting light in the first predetermined rangeof wavelengths; a plurality of optical elements arranged such that (a)light emitted from the at least one illumination source is directed tothe alkali vapor cell, and (b) light emerging from the alkali vapor cellis directed to the light collector; a generally planar electricalinsulator having a top and a bottom, the top and the bottom beingopposed to one another; a top trace on the top of the insulator; abottom trace on the bottom of the insulator; and a through trace, theinsulator defining a via from the top to the bottom, the through tracecontacting both the top trace and the bottom trace and passing throughthe via so that the top trace, bottom trace and through trace form asingle electrically conductive element; wherein the top trace and thebottom trace are congruent so that a current along the singleelectrically conductive element tends to create a self-cancellingmagnetic field.
 3. The assembly of claim 1 further comprising: agenerally planar electrical insulator having a top and a bottom, the topand the bottom being opposed to one another; a top trace on the top ofthe insulator, the top trace having a top trace height and a top tracewidth; and a bottom trace on the bottom of the insulator, the bottomtrace having a bottom trace height and a bottom trace width; wherein:the ratio of the top trace height to the top trace width and the ratioof the bottom trace height to the bottom trace width both being in therange of 0.5 to 2; and the top trace and the bottom trace are congruentso that when equal and oppositely directed currents exist simultaneouslyin the top trace and the bottom trace, the equal and oppositely directedcurrents tend to create cancelling magnetic fields.
 4. The assembly ofclaim 2 wherein the top trace, or the bottom trace, or both, are inthermal contact with the alkali vapor cell such that when current ispassed through the electrically conductive element, thereby producingheat, the heat is transferred to the alkali vapor cell.
 5. The assemblyof claim 2 wherein the top trace, or the bottom trace, or both are notsubstantially in thermal contact with the alkali vapor cell.
 6. Theassembly of claim 2 further comprising an optical heating element and aheat illumination source configured to emit light having a secondpredetermined range of wavelengths when activated, wherein: the opticalheating element is in thermal contact with the alkali vapor cell; theoptical heating element includes a light-absorbing material that absorbslight in at least a portion of the second predetermined range ofwavelengths; and the plurality of optical elements are arranged suchthat at least some light emitted from the heat illumination source isdirected to the optical heating element.
 7. The assembly of claim 6wherein: the optical heating element defines an internal cavity; andsubstantially all of the at least some light emitted from the heatillumination source is directed to the internal cavity.
 8. The assemblyof claim 7 wherein the internal cavity is defined at least in part by aninternal surface, the internal surface including at least a portion ofthe light-absorbing material.
 9. The assembly of claim 8 whereinsubstantially all surfaces defining the internal cavity are covered inthe light-absorbing material such that substantially all of the lightemitted from the heat illumination source and directed to the internalcavity is absorbed by the optical heating element.
 10. The assembly ofclaim 7 wherein light-absorbing material is disposed on a surface of theoptical heating element that does not define any portion of the internalcavity.
 11. The assembly of claim 7 wherein the internal cavity is ablind bore.
 12. The assembly of claim 7 wherein the internal cavity is apolygonal prism.
 13. The assembly of claim 6 wherein the optical heatingelement includes on at least a portion of the interior surface amaterial that reflects light in at least a portion of the predeterminedrange of wavelengths.
 14. The assembly of claim 7 wherein a portion ofthe internal cavity is defined by a material that is (a) substantiallytransparent to light in at least a portion of the predetermined range ofwavelengths and (b) substantially absorbent to light in a differentwavelength range.
 15. The assembly of claim 6 further comprising: atemperature sensor configured to sense the temperature at apredetermined location on the assembly; and a controller that is:configured to receive from the temperature sensor signals indicative ofthe temperature at the predetermined location on the assembly; operablyconnected to the at least one heat illumination source; and configuredto activate the at least one illumination source so as to illuminate theheating element.
 16. The assembly of claim 15 wherein the temperaturesensor includes substantially no electrical currents.
 17. The assemblyof claim 6 wherein the first predetermined range of wavelengths and thesecond predetermined range of wavelengths are identical.
 18. Theassembly of claim 6 wherein the first predetermined range of wavelengthsand the second predetermined range of wavelengths have some wavelengthin common but are not identical.
 19. The assembly of claim 6 wherein thefirst predetermined range of wavelengths and the second predeterminedrange of wavelengths have no wavelength in common.
 20. The assembly ofclaim 2 further comprising: an electrical insulator having a surface;and a trace on the surface of the insulator; wherein the trace isconfigured so that, when a predetermined current is passed through thetrace, a magnetic field having a desired predetermined geometry andmagnitude is created.
 21. The assembly of claim 20 wherein the desiredpredetermined geometry and magnitude substantially cancels a backgroundmagnetic field in a predetermined volume that includes at least aportion of the assembly.
 22. The assembly of claim 21 wherein thebackground magnetic field is manmade.
 23. The assembly of claim 21wherein the background magnetic field is the earth's magnetic field. 24.An assembly for use in a high-sensitivity atomic sensor, the assemblycomprising: an alkali vapor cell; at least one illumination sourceconfigured to emit light when activated, the emitted light having afirst predetermined range of wavelengths; a light collector capable ofcollecting light in the first predetermined range of wavelengths; aplurality of optical elements arranged such that (a) light emitted fromthe at least one illumination source is directed to the alkali vaporcell, and (b) light emerging from the alkali vapor cell is directed tothe light collector; an electrical insulator having a surface; and atrace on the surface of the insulator; wherein the trace has afilamentary structure comprising a plurality of electrically insulatedsub-traces.
 25. The assembly of claim 24 wherein the filamentarystructure is configured to minimize magnetic field fluctuation in apredetermined volume that includes at least a portion of the assembly.26. (canceled)
 27. (canceled)